On a long inhale, say "health in."
On a long exhale, say "cancer out."
Repeat as long as you want. I usually did this for about 10 repetitions a time and, if I were really focusing well, I honestly could envision good, clean white air going in, and the evil cancer going out. I still occasionally do this, five years later.
Now, I seldom mention cancer, I just repeat "health in" on the inhale, and simply relax on the exhale.